#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>

#define BUF_SIZE 100

void error_handling(char *msg);

int main(int argc, char *argv[])
{
    int fd;
    char buf[BUF_SIZE];

    fd = open("data.txt", O_RDONLY);
    if (fd == -1) {
        error_handling("open() error");
    }
    printf("file descriptor: %d\n", fd);

    if (read(fd, buf, sizeof(buf)) == -1) {
        error_handling("read() error");
    }
    printf("file data: %s", buf);
    close(fd);

    return 0;
}

void error_handling(char *msg)
{
    fputs(msg, stderr);
    fputc('\n', stderr);
    exit(1);
}